Check your Holdings screen. Did you set up the Vanguard Prime Money Market Fund as a mutual fund? If so Q does not see this as cash. You will need to enter a Sell transaction @ $1/sh from the MMF first to create a cash balance.Or, and this is my preference, simply ignore the MMF as a fund and treat it as cash. Sell all shares of the fund @ $1 and leave the cash balance in your Q account register. If you download from Vanguard in the future you would have to change the ReinvDiv to just Div to keep the balance accurate, but this eliminates the need to enter Sells every time you make a purchase.Does that solve it?